1. Field
This invention relates generally to percussive devices and more particularly to a novel impulser for percussively loading a structure to generate stress waves in the structure.
2. Prior Art
As will appear from the ensuing description, the impulser of the present invention may be used for a variety of purposes. The principal application of the impulser, however, is in the holographic instrument described in the above mentioned copending application Ser. No. 598,901. The latter application describes a holographic instrument which may be used as an optical signature instrument to determine the structural integrity of a structure, such as an aircraft, by percussively loading the structure to generate stress waves in the structure and recording two successive holograms of the structure on the same holographic recording medium in timed relation to propagation of the stress waves through the structure. These stress waves produce varying stress conditions in the structure with the result that the two successive holograms are recorded under different stress conditions in the structure. Accordingly, the resulting double exposure hologram constitutes a holographic interferrogram containing a deformation fringe pattern representing the deformational displacements produced in the structure by the change in stress conditions between the two holograms.
As described in the application, interferrograms produced in this way at different times but under the same stress conditions may be compared to evaluate the structural integrity of the structure by determining changes, if any, in the interferrogram fringe patterns. Such fringe pattern changes are indicative of changes in the structural integrity due to fatigue damage, stress corrosion cracking, and other causes.
Satisfactory operation of the optical signature instrument requires percussive loading of the structure with the same force each time the structure is inspected and recording of the two holograms during each inspection in precise timed relation to application of the percussive load. In some applications, the structure being inspected must be protected against damage by the percussive loading means.